It is frequently necessary to signal certain operating states of systems. If these systems are operated in a normal environment that is not potentially explosive, this is simply accomplished with light-emitting diodes that are arranged on the device. However, the situation is more complicated if the system components are encapsulated due to a potentially explosive atmosphere. When signaling devices are arranged outside the explosion protection housing, the electric lines need to be routed through the wall of the housing often in difficult and elaborate fashion. While it would be easier to accommodate the signaling device with the housing, this would create a visibility problem.
It is further known to fit the explosion protection housing with transparent panes, through which readings of measuring devices located behind the panes can be made. However, transparent materials are not as strong as the remaining material of the housing, which becomes a particularly troublesome factor if the transparent pane occupies a large area. The larger the surface area of the transparent pane, the more difficult it is to ensure its resistance to breaking from pressure occurring when an explosion within the interior of the housing takes place.
If a light-emitting diode wire were arranged in the housing as a light source, in that case, a slender rod of transparent material would, in principle, suffice for rendering the light source or the light-emitting diode visible from outside the housing. However, the small angle at which the light emerges is disadvantageous to that approach. Another troublesome factor is that the light originating from the light source or the light-emitting diode is emitted in a divergent fashion. Only part of this type of light would be totally reflected on the cylindrical outer surface of the rod-shaped optical waveguide. Since a majority of the emitted light would be absorbed at this location, the luminous efficiency is inferior or inadequate.